1. Field of the Invention
The present invention relates to an electron gun for a color cathode ray tube, and more particularly, to an electrode of an electron gun for a color cathode ray tube which can extend an electric field for forming an electronic lens.
2. Description of the Related Art
In a general electron gun for a color cathode ray tube, spherical aberration and focusing characteristics are greatly affected by a main lens. Thus, in order to obtain good focusing characteristics, the spherical diameter of the main lens must be increased. Also, in order to reduce deflection power, it is preferable to reduce the diameter of the neck portion of a cathode ray tube. In this case, the area in which electron beam passing apertures of an electrode are located is decreased. It is necessary to increase the area of the electron beam passing apertures as much as possible in a limited area.
However, in an in-line electron gun, since three electron beam passing apertures are formed at at least two electrodes constituting an electronic lens in an in-line configuration, it is impossible to make the diameter of an electron beam passing aperture larger than a distance between centers of two adjacent electron beam passing apertures.
An electrode for solving the above-described problem is disclosed in U.S. Pat. No. 4,510,413. This electrode comprises a flat portion 11 having three electron beam passing apertures RH, GH and BH, a cylindrical skirt portion 12 extending from the edge of the flat portion 11, and an embedded portion 13 extending from an end of the skirt portion 12 in a radial direction, as shown in FIG. 1. A tapering portion 14 leading to the flat portion 11 is formed at the edges of the respective electron beam passing apertures RH, GH and BH.
In the above-described electrode, the tapering portion 14 extends the electric field to increase the area of an electronic lens. However, since the electron beam passing apertures RH, GH and BH are independently formed, the effect of increasing the electronic lens is not satisfactory.
FIG. 2 shows an example of an electrode for forming a large-diameter lens, which is disclosed in U.S. Pat. No. 4,370,592.
As shown in FIG. 2, burring portions 5b and 6b are formed at edges of an electron outlet surface 5a of a focusing electrode 5 and an electron inlet surface 6a of a final accelerating electrode 6, and large-diameter electron beam passing apertures 5H xe2x80x2 and 6H xe2x80x2 through which R, G and B electron beams pass commonly by slanted surfaces 5c and 6c recessed a predetermined depth from the burring portions 5b and 6b. R, G and B small-diameter electron beam passing apertures are formed adjacent the slanted surfaces 5c and 6c. 
According to the above-described electrode, an electric field can be extended by the large-diameter electron beam passing apertures 5H and 6H. However, a continuously smooth electric field cannot be formed around the burring portions 5b and 6b. This finally distorts the electronic lens formed by the electric field.
In particular, since the small-diameter electron beam passing apertures 5H xe2x80x2 and 6Hxe2x80x2 are formed adjacent the slanted surfaces 5c and 6c, there is a limit in increasing the eccentric distance between the small-diameter electron beam passing apertures 5H xe2x80x2 and 6Hxe2x80x2.
To solve the above problems, it is an objective of the present invention to provide an electrode of an electron gun for a color cathode ray tube which can reduce spherical aberration and improve focusing characteristics, by extending an electric field for forming a main lens.
Accordingly, to achieve the above objective, there is provided an electrode of an electron gun for a cathode ray tube comprising a first electrode member having a large-diameter electron beam passing aperture through which three electron beams pass, and a second electrode member installed in the first electrode member so as to be spaced apart from the edge of the first electrode member and having three small-diameter electron beam passing apertures, wherein a slant portion is formed to extend from the edge of the first electrode member toward the interior of the large-diameter electron beam passing aperture.
Also, slant surfaces extending to the surface of the second electrode member are formed at circumferences of the small-diameter electron beam apertures of the second electrode member.
According to another aspect of the present invention, an electrode of an electron gun for a cathode ray tube comprising a first electrode member having a large-diameter electron beam passing aperture through which three electron beams pass and a burring portion formed at the edge of the large-diameter electron beam passing aperture, and a second electrode member installed in the first electrode member so as to be spaced apart from the burring portion and having three small-diameter electron beam passing apertures, wherein slant surfaces extending to the surface of the second electrode member are formed at the circumferences of the small-diameter electron beam passing apertures of the second electrode member.